John,
I found the source of the 10.7 MHz spur. It's being generated inside the
receiver itself. This is the first spur I have found that is not caused by
switching power supplies.
The origin appears to be in the 10 MHz reference area. I turned off and
unplugged the SDR-IQ and fed the IF output from the 70 cm Receiver to my
TS-2000. The spur is still there.
Next I connected the RF input to my sniffer loop and moved it around the PCB
surface. I get the strongest signal near the long trace between the two
Freq inputs to U4 and U9, the two phased-locked loops.
73,
Juan